PGRMC1 und PLOD2 steuern die Interaktion zwischen Tumorzellen und neutrophilen Granulozyten in der Mikroumgebung des Glioblastoms

Accumulating evidence indicates that glioblastoma (GBM) microenvironment contains significant numbers of infiltrating neutrophil granulocytes, which interact with the GBM cells in a bi-directional manner to promote tumor progression. The mechanisms of these interactions are poorly understood thus far. Our study aimed to characterize the effect of GBM cells on key biological functions of neutrophils that are typically associated with a pro-tumor phenotype. In this context, we assessed the roles of PGRMC1 and PLOD2, as these factors were recently linked to GBM progression and the poor outcome of GBM patients.

The functional studies were performed on peripheral blood neutrophils isolated from healthy donors and stimulated ex vivo with supernatants from two different GBM cell lines (H4 and U251). The neutrophils were additionally stimulated with supernatants from H4 and U251 cells stably transfected to downregulate PGRMC1 and PLOD2. The in situ studies were performed on tissue microarrays from patients with confirmed IDH wild-type GBM (n=279).

GBM supernatants induced neutrophil recruitment (chemotaxis), prolonged their survival and promoted the release of MMP9 by neutrophils. The supernatants from PGRMC1 knock-down GBM cells had a markedly weaker chemotactic effect on neutrophils, which was a consequence of reduced CXCL8 levels. These findings were supported by in situ studies, where we found a significant correlation between the numbers of tumor-infiltrating neutrophils and the levels of PGRMC1 in the tumor cells. While PGRMC1 knock-down did not affect neutrophil survival or the release of MMP9, PLOD2 knock-down suppressed the stimulatory effect of GBM cells on both neutrophil functions. In line with these findings, GBM patients with synchronous high levels of PLOD2 and neutrophil infiltration had a significantly shorter overall survival compared to the other groups of patients.

Our study shows that GBM cells release soluble factors which can recruit neutrophils to the tumor tissue and induce them to aquire tumor-promoting functions. The recruitment of neutrophils is mediated via a PGRMC1-CXCL8 axis, while PLOD2 mediates the release of -yet unidentified- factors that stimulate neutrophils to produce high levels of pro-angiogenic and pro-invasive MMP9. These findings contribute to a better understanding of GBM pathophysiology and may foster the development of novel therapeutic strategies against these tumors.